1. Field of the Invention
The present invention relates to a non-destructive means for detecting defects, such as voids, or poorly adhering layers in solid objects and laminated materials. More specifically, the instant invention relates to an ultrasonic scanning arrangement which includes ultrasonic emitting and receiving transducers which are disposed in a housing, and via which an object can be non-invasively inspected for defects.
2. Description of the Prior Art
In the art of ultrasonic detection, various methods are known for non-destructively inspecting solid objects. Among these methods are an ultrasonic transmission technique, a reflection technique, and an ultrasonic resonance technique. One or more of the above methods is selected, depending usually upon the test conditions, and the number of transducers to be used in the test device.
The sensing methods may be further sub-divided into a so called vertical method, angular method, immersion method, panel wave method, surface wave method, transmission method, thickness detection method, the holographic imaging method, and the defect detection arrangement method.
Some prior art detection methods are disclosed in detail in The Third Edition of The Steel handbook Volume IV "Alloys: Tests and Analysis" Oct. 30 1972, Published by Maruzen Co. Ltd. on pages 447-448 under the heading "Non-destructive Tests".
In FIG. 1 an example is given of a sensor assembly 51 according to the prior art. A housing unit 52, includes an insulating member 53 which is disposed in the blind end of a elongate bore, a spring 54 and an ultrasonic transducer 55. The spring is arranged to bias the ultrasonic transducer 55 against an object 11 under test.
Within the interior of the housing unit 52, a lateral buffer member 56 is disposed, which serves to maintain the in position while insulating the housing unit 52 from the ultrasonic transducer 55.
In detection operations using the FIG. 1 device, it is common to use the resonance method or the reflection method. On the other hand, in cases where two transducers are provided, it is known to employ the transmission technique.
As is well known, with these methods, the reflected or the transmitted signals and/or resonance frequencies are analyzed in order to determine the characteristics of the object to be tested. In the above techniques however, problems have been encountered in that the strength, and general characteristics of the received measurement signals are rather strongly influenced by the pressure with which the transducer assembly is maintained in engagement with the object to be tested. For this reason, considerable skill on the part of the operator, has been required in order to obtain reproducible readings. This has tended to limit the applicability of these methods and has prevented more general use.
Accordingly, there has been a need to provide a technique of holding an ultrasonic transducer in engagement with an object to be tested in a manner which alleviates the need for a high level of skill on the part of the operator.
Another disadvantage encountered in the ultrasonic sensing devices of the prior art lies in the fact that, a single transducer is usually used for both emitting and receiving the inspection signal. Because of this double function, compromises must be made in the construction of the transducer, in order to allow it to serve equally well as an emitter and receiver. Another problem with this arrangement is that the transducer must be switched very rapidly between the emitting and receiving modes, and thus renders the signal sending and receiving sections of the control device, complex.
In view of the above problems, a method, which is disclosed in JP-A-63-120252, was developed for detecting the presence or absence adhesion between the layers of laminated material, and for determining the bonding strength of an adhesive when it is present.
In the above disclosed device the problem remains that a rather high level of skill is still required of the user, in order to obtain satisfactory reproducible results.